This invention relates to a composite material which is made up of a fluororesin and glass fiber and possesses good flexibility and heat processability. The fluororesin used as the matrix is a graft copolymer having an elastomeric "trunk" segment and a crystalline "branch" segment.
Glass fiber reinforced plastics are used for many purposes and in various forms including sheet form, and the matrix material is selected from various resins such as polypropylene resins, polyester resins, polyamide resins, polyvinyl chloride resins and fluororesins with consideration of physical and chemical properties required for the composite materials and also economical factors.
Fluororesins are superior to other kinds of resins in weather resistance, chemical resistance and burn resistance because of having C-F bond very high in bond energy. Accordingly fluororesins are regarded as advantageous matrix materials for glass fiber reinforced composite sheets which may be used, for example, as wall facing materials, as anticorrosive lining materials for various vessels or containers, as wrapping and packaging materials, as electrical insulating materials and as tent materials. However, conventional fluororesins have some disadvantages in being used in the form of glass fiber reinforced resin sheet. First, conventional fluororesins other than fluororubbers are poor in flexibility so that the glass fiber reinforced composite sheets become stiff to the touch. Second, most of conventional fluororesins are not good in melt processability so that complicated techniques are required for embedding glass fiber in such resins. Besides, in the cases of conventional fluororesin sheets it is difficult to join or laminate a plurality of pieces of sheets by a high-frequency welding method which is the most convenient method for ordinary resin sheets.
In conventional fiber reinforced fluororesins a representative of the matrix resins is polytetrafluoroethylene (PTFE), which is hardly extrudable since its melting temperature is as high as about 330.degree. C. Therefore, glass fiber reinforced PTFE sheets are usually produced by first impregnating glass fiber with a dispersion of PTFE and then performing a pressure shaping operation. When polyvinylidene fluoride (PVDF) having a lower melting temperature, about 171.degree. C., is used as the matrix polymer it is possible to produce a glass fiber reinforced resin sheet by rolling a PVDF film extruded from a conventional extruder together with a glass fiber cloth. However, glass fiber reinforced PVDF sheets as well as glass fiber reinforced PTFE sheets lack flexibility.